I think that the simplest answer to that question is that, unless all 4 paths are operating at 100% throughput, losing a path will not have any effect on performance...
HBA's are rarely operating at 100% throughput constantly unless it is an extremely IO intensive environment.
To see what kind of throughput your HBA;s are operating at use the usual performance tools like iostat and sar -d
I mostly agree with your statement here Conor, except that with 4 HBAs, you would be looking for 75% utilization on all four (not 100%). If they were all running at 75% and you lost one, that would redistribute the 75% from that one to the other three driving them up to 100% (which we can probably all agree wouldn't be healthy).
In order to determine the threshold you would have to calculate the maximum sustained rate you want a single port to run at and them balance the load to ensure that you never go over that even with one path down.
Now, having said that it is still highly dependant on the answer to Dynamox's question: What is the array?
If you are connected to a Symm (with active/active pathing) then this is true. If you are connected to a CLARiiON (with active/passive pathing) then it is a whole different ballgame.
On a CLARiiON, only two of your four paths will be active. A failure on one path will drive all the I/O down another path. You would have to have a failure on two paths to the same SP in order to fail over to the other two paths (on the other SP). In this case you should never drive your HBAs beyond half the maximum capacity you ever want to push through.
dynamox
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April 9th, 2009 04:00
Conor
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April 9th, 2009 06:00
HBA's are rarely operating at 100% throughput constantly unless it is an extremely IO intensive environment.
To see what kind of throughput your HBA;s are operating at use the usual performance tools like iostat and sar -d
SKT2
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April 9th, 2009 10:00
Allen Ward
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April 13th, 2009 09:00
In order to determine the threshold you would have to calculate the maximum sustained rate you want a single port to run at and them balance the load to ensure that you never go over that even with one path down.
Now, having said that it is still highly dependant on the answer to Dynamox's question: What is the array?
If you are connected to a Symm (with active/active pathing) then this is true. If you are connected to a CLARiiON (with active/passive pathing) then it is a whole different ballgame.
On a CLARiiON, only two of your four paths will be active. A failure on one path will drive all the I/O down another path. You would have to have a failure on two paths to the same SP in order to fail over to the other two paths (on the other SP). In this case you should never drive your HBAs beyond half the maximum capacity you ever want to push through.
Complicated enough?
Conor
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April 13th, 2009 12:00
Cheers
Conor
Allen Ward
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April 14th, 2009 10:00